A Study to Investigate the Safety and Efficacy of KQB368 as Monotherapy in Participants With Advanced Solid Malignancies

The goal of this study is to learn if KQB368 works to treat advanced solid malignancies in adults. The study will also learn about the safety of KQB368. The main questions the study aims to answer are: * What is the safe dose of KQB368 as a monotherapy? * Does KQB368 decrease the size of the tumor? * What happens to KQB368 in the body? Participants will: * Take KQB368 orally daily in 21-day cycles * Return to the study site about 7 times in the first 5 weeks, and then once at the beginning of every 21-day cycle after that

* Histologically confirmed diagnosis of a solid tumor * Malignancy with either a KRAS G12C or KRAS G12S mutation * Unresectable or metastatic disease * No available treatment with curative intent * Adequate organ function * Measurable disease per RECIST v1.1 * Must be able to swallow with no GI condition that prevents absorption